.container{
    width: 600px;
    margin: 0 auto;
    text-align: center;
}

.input_container{
    margin-top:4px;
}

.btn{
    width: 80px;
    padding: 2px 8px;
    height: 30px;
    border:1px solid transparent;
    border-radius: 4px;
}

.diffculty{
    width: 60px;
    padding: 2px 4px;
    height: 30px;
}

input[type=text]{
    width: 60px;
    padding: 2px 4px;
    height: 24px;
}

table {
    border-collapse: collapse;
    margin: 0 auto;
    margin-top: 4px;
}

table tr td{
   border:1px solid #ffffff; 
   background-color: #00ff35;
   width: 50px;
   height: 50px;
}